As eco-friendly vehicles, electric vehicles and hybrid vehicles are being increasingly used. On such a vehicle, a power supply apparatus configured by battery assemblies in each of which a plurality of batteries are stacked on one another is mounted.
In order to connect in series the battery assemblies configured by stacking in alternately opposite directions, the batteries of the power supply apparatus are connected to one another by bus bars each having two holes through which electrodes (terminals) of adjacent batteries are passed through, respectively, and, in order to detect the voltage of each battery, a signal line which is connected to each bus bar to output the voltage of the battery to the outside is wired to the bust bar (for example, see Patent Document 1).